Corresponding Author: Kyungmin Koh, MD, PhD, MBA. Department of Ophthalmology, Kim’s Eye Hospital, Konyang University College of Medicine, 136 Yeongshin-ro, Yeongdeungpo-gu, Seoul 07301, Korea. The increased life expectancy and dramatically improved cataract surgery techniques have led to an increase in number of patients undergoing cataract surgery [1]. The changing lifestyles and advancement in technology have resulted in growing demand for improved visual acuity (VA) without glasses at all distances through cataract surgery [2]. To meet these needs, various multifocal and extended depth of focus (EDOF) intraocular lenses (IOLs) have been introduced [3,4]. Multifocal IOLs have two or more foci for reducing dependence on spectacle after surgery [5]. Despite their ability to divide light and produce specific focal spots, multifocal IOLs can also have negative effects on contrast sensitivity and increase unwanted photic phenomena [6]. To minimize such shortfalls of multifocal IOLs, EDOF IOLs with good functional vision range and improved contrast sensitivity have been introduced [7]. EDOF IOLs offer a continuous range of vision with reduced incidence of undesirable photic phenomena [7]. While EDOF IOLs are beneficial, it has been reported that they do not perform as well as conventional multifocal IOLs in terms of near VA [8-10].
Previous research has revealed that the mini-monovision method can improve near VA after bilateral EDOF IOL implantation compared to the traditional method that focuses on emmetropia for both eyes [11-13]. These research have indicated short-term VA outcomes, which range from 1 to 6 months after surgery [11-13].
The objective of our study was to assess the long-term effectiveness of the mini-monovision procedure with globally renowned EDOF IOL, Tecnis Symfony ZXR00 (Johnson & Johnson Vision).
Materials and Methods
Ethics statement
The study was approved by the Institutional Review Board of Kim’s Eye Hospital (No. 2023-07-002). The requirement for informed consent was waived due to the retrospective nature of the study. The study was conducted in accordance with the principles of the Declaration of Helsinki.
Participants
This retrospective, single center, nonrandomized study conducted in Kim’s Eye Hospital (Seoul, Korea). Cataract patients bilaterally implanted with ZXR00 in both eyes using the mini-monovision method (target refraction of −0.3 diopters [D] in the dominant eye and −0.6 D in the nondominant eye) between April 2019 and March 2021 were examined. Before surgery, all patients were provided with information about the risks and benefits of implanting bilateral ZXR00s using the mini-monovision method. The study involved patients older than 40 years with follow-up period of over 2 years. The exclusion criteria comprised of the following: any systemic or ocular conditions (except for cataract) with the potential to result in VA loss, any intraoperative or postoperative complications that could affect visual outcomes, previous history of intraocular/corneal/refractive surgery, and corneal astigmatism of more than 1.00 D.
The VA was taken with the ETDRS (Early Treatment Diabetic Retinopathy Study) test in logarithm of the minimum angle of resolution (logMAR) scale. Uncorrected distance VA (UDVA) and corrected distance VA (CDVA) were evaluated at 6 m, uncorrected intermediate VA (UIVA) was measured at 66 cm, and uncorrected near VA (UNVA) was evaluated at 40 cm.
IOL power calculation and target spherical equivalent (SE) was derived from The Barrett Universal II formula of a high-resolution anterior segment swept-source optical coherence tomography (Anterion, Heidelberg Engineering GmbH). The IOL power was calculated with target SE closest to −0.3 D for dominant eye and −0.6 D for nondominant eye. The difference between the actual postoperative manifest refraction SE (MRSE) and target SE was determined as refractive error (RE) [14]. The mean absolute value of RE was determined as the mean absolute error (MAE) [15].
Intraocular lenses
The standard aim of the Tecnis Symfony EDOF IOL (ZXR00) is to expand the depth of focus allowing a wide range of vision [16]. It received the European Conformité Européenne (CE) mark approval in 2014 and the US Food and Drug Administration (FDA) approval in 2016. ZXR00 has a diffractive echelette design posterior surface with nine diffractive rings [17]. Besides the aspherical anterior surface with a spherical aberration of 0.27 μm, it also has a posterior achromatic design for correcting chromatic aberrations [18].
Surgical procedures
All surgical procedures were performed by a single experienced surgeon (KK) using a single device (Whitestar Signature Phacoemulsification System, Johnson & Johnson Vision). Main corneal incision was made in the steep meridian using a 2.8-mm keratome, and a capsulorhexis was created measuring approximately 5.2 mm. Wound hydration without suture was done after removing an ophthalmic viscosurgical devices (Provisc, Alcon Laboratories).
Statistical analysis
A statistical analysis of the data was conducted using a software program IBM SPSS ver. 22.0 (IBM Corp). Five statistical tests were employed to confirm the normality of data distributions and to verify differences between separate groups of data, including Kolmogorov-Smirnov test, Mann-Whitney U-test, unpaired student t-test, Wilcoxon signed rank test, and McNemar test. The statistical significance of the p-value was determined to be lower than 0.05.
Results
Our study consisted of 122 eyes from 61 patients who received bilateral implantation of ZXR00 with mini-monovision approach (dominant eye targeted for −0.3 D and nondominant eye for −0.6 D). The average age of the patients was 61.8 ± 7.7 years (range, 43-81 years), in which 36 patients (59.0%) were female (Table 1). Preoperative features for dominant and nondominant eyes are presented in Table 1. The preoperative features did not show any significant difference between dominant eyes and nondominant eyes except for mean target SE (p < 0.001), which was intentionally set differently with mean target SE of −0.32 ± 0.21 in the dominant eye and −0.64 ± 0.25 in the nondominant eye to achieve mini-monovision.
The results of monocular postoperative VA assessment are shown in Table 2. Monocular UDVA and CDVA at 3 months and 2 years after surgery showed excellent results. At 3 months postoperatively, monocular UDVA and CDVA were 0.01 ± 0.02 and 0 ± 0 logMAR, respectively, in the dominant eye, and 0.02 ± 0.03 and 0 ± 0 logMAR, respectively, in the nondominant eye. At 2 years postoperatively, these values were 0.11 ± 0.10 and 0.01 ± 0.03 logMAR, respectively, in the dominant eye, and 0.12 ± 0.12 and 0.01 ± 0.03 logMAR, respectively, in the nondominant eye.
Mean MRSE at 3 months after surgery were −0.31 ± 0.38 in the dominant eye and −0.53 ± 0.47 in the nondominant eye, while mean MRSE at 2 years after surgery was −0.38 ± 0.43 in the dominant eye and −0.61 ± 0.54 in the nondominant eye (Table 2). Mean MRSE for the nondominant eye showed statistical significance (p = 0.001) between short- and long-term follow-up, with 2 years postoperative result being more myopic and closer to the targeted SE of −0.60. Mean MRSE for the dominant eye also showed myopic shift at 2 years after surgery, yet statistical significance was not reached (p = 0.538). RE of the dominant eye was 0.01 ± 0.39 at 3 months and −0.06 ± 0.43 at 2 years while that of the nondominant eye was 0.15 ± 0.49 at 3 months and 0.05 ± 0.57 at 2 years after surgery. MAE was 0.29 ± 0.26 at 3 months and 0.32 ± 0.29 at 2 years after surgery for the dominant eye. As for the nondominant eye, MAE was 0.38 ± 0.34 at 3 months and 0.43 ± 0.37 at 2 years after surgery. RE for the nondominant eye revealed signif icantly smaller value at long-term follow-up (p = 0.009) while MAE showed no difference among the follow-up period regarding both dominant and nondominant eyes.
Binocular postoperative UDVA and CDVA also showed outstanding results for both follow-up periods (Table 3). At 3 months postoperatively, the mean postoperative binocular UDVA and CDVA were 0.007 ± 0.019 and 0 ± 0 log-MAR, respectively; at 2 years postoperatively, these values were 0.086 ± 0.094 and 0.012 ± 0.024 logMAR, respectively. Mean postoperative binocular UIVA at 66 and 40 cm were 0.047 ± 0.041 and 0.178 ± 0.049 logMAR, respectively, at 3 months after surgery and 0.056 ± 0.041 and 0.140 ± 0.045 logMAR, respectively, at 2 years after surgery. Comparison of short- and long-term results showed that UDVA (p < 0.001), CDVA (p = 0.001), and UIVA at 66 cm (p = 0.040) were significantly superior at 3 months following surgery. On the other hand, UNVA at 40 cm was significantly better at 2 years postoperatively (p < 0.001).
Three months after surgery, eight out of 61 patients (13.1%) needed near glasses. This rate rose to nine out of 61 (14.8%) at 2 years after surgery, which was not a significant change (p = 0.998).
Discussion
One of the main hesitations in choosing ZXR00 is poor near VA, as evidenced by high postoperative spectacle dependence for near vision in previous studies with standard bilateral ZXR00 implantation targeting emmetropia. A study in 2019 by Son et al. [19] reported spectacle dependence for near vision of 25%; a study in 2019 by Tan et al. [20] reported spectacle dependence of 71.43%; and a study in 2020 by Kim et al. [21] reported spectacle dependence of 50.0% for near vision.
The mini-monovision method with ZXR00 was introduced to overcome this problem. Previous research on ZXR00 mini-monovision have revealed that 19% of patients required near-sight glasses 4 to 6 months after surgery [22] and 16% at 6 months after surgery [23]. Results from our study showing a rate of near-sight spectacle dependence of 13.1% at 3 months and 14.8% at 2 years after surgery. Our study revealed a decreased likelihood of needing spectacles for near vision after surgery compared to previous studies on ZXR00 mini-monovision. This may be attributed to the fact previous studies on ZXR00 mini-monovision targeted dominant eye for emmetropia and nondominant eye for about −0.50 to −0.75 D [20,22,23] while we targeted dominant eye for −0.3 D and nondominant eye for −0.6 D. Therefore, when performing mini-monovision with EDOF IOLs, targeting the dominant eye for slightly myopic refraction may help achieve highest spectacle independence for near vision after surgery.
Previous studies on bilateral ZXR00 implantation targeting emmetropia have shown less favorable results for near vision; Tan et al. [20] reported binocular UNVA of 0.52 ± 0.36 logMAR and Pedrotti et al. [24] reported UNVA of 0.26 ± 0.08 logMAR at 3 months after surgery. In comparison, our study showed excellent binocular VA results at all measured distances at 3 months postoperatively; binocular UDVA, UIVA, and UNVA were 0.007 ± 0.019, 0.047 ± 0.041, and 0.178 ± 0.049 logMAR, respectively, which were all under 0.2 logMAR. The excellent VA results shown in our study were maintained at 2 years after surgery with UDVA, CDVA, and UIVA all under 0.06 logMAR and UNVA under 0.15 logMAR. The VA results obtained in our study (implantation of ZXR00 using a mini-monovision method, target refraction of −0.3 D in the dominant eye and −0.6 D in the nondominant eye) offer excellent distant and intermediate vision, but also adequate near vision.
Our results indicate that mini-monovision with ZXR00 allows for excellent VA from far to near distance at both short- and long-term follow-up periods after surgery. Considering that previous research on ZXR00 mini-monovision consisted of short-term outcomes at 1 to 6 months after surgery, our study provides further insight into longer postoperative VA outcomes at 2 years after surgery.
In a study that investigates the mix-and-match of ZXR00 and bifocal IOL (Tecnis ZLB00, Johnson & Johnson Vision), UNVA at 3 months postoperatively was 0.099 ± 0.068 logMAR and spectacle dependence for near vision was 10.7% [25]. This result is similar to our study with spectacle dependence for near vision of 13.1% at 3 months postoperatively and 14.8% at 2 years postoperatively. Therefore, either hybrid monovision with ZXR00 and bifocal IOL or ZXR00 mini-monovision with target of −0.3 D in the dominant eye and −0.6 D in the nondominant eye may allow spectacle dependence around early 10% alike.
Growing demand in recent years for good intermediate VA for smartphones and computer has led to the development of trifocal lens with not only near and far foci like previous lenses but also with intermediate focus [26]. However, as we know, increasing number of foci dividing the light may cause more glares and halo, increased loss of transmitted light, and decreased contrast sensitivity [27]. Common complaints after multifocal IOL surgery include waxy vision (58%), glare and halo (30%), blurring of distant vision (24%), blurring of near vision (18%), and dysphotopsia (20%) [27]. To overcome such shortfalls of multifocal IOLs, EDOF IOLs with a single extended focus rather than multiple foci have been developed. Because EDOF IOLs do not divide light into separate foci, photic phenomena are lower [7]. In a 2019 study on patients with ZXR00 implantation [28], 18% of the patients experienced mild postoperative photic phenomena, of which 13% were halo. In another study comparing trifocal and EDOF IOLs [29], photic phenomena after ZXR00 implantation (14%) were less than half the incidence of photic phenome after trifocal IOL implantation (38%).
Only a handful of studies have examined long-term clinical results after ZXR00 IOL implantation. A newly published study [30] found that, after 2 years, ZXR00 maintained superior intermediate VA relative to monofocal IOLs and visual function comparable to that of eyes with monofocal IOLs. Likewise, our study also showed that bilateral implantation of ZXR00s with mini-monovision leads to an excellent VA at far, intermediate, and near distances over 2 years after surgery.
A decrease in VA at 2 years after surgery compared to 3 months after surgery seen in our study may be due to several factors. First, there is a long gap of 21 months between the two follow-up time points, the occurrence of posterior capsular opacification may have contributed to the decrease in VA. Posterior capsular opacification has been shown to occur up to 20% to 40% within 5 years after surgery, rendering it as one of the most common complication following cataract surgery [31]. A study involving monofocal IOL (ZCB00, Johnson & Johnson Vision) from the same platform as ZXR00 [32] demonstrated that 26.1% of eyes required neodymium:yttrium-aluminum-garnet (Nd:YAG) capsulotomy 3 years after implantation.
This study has several limitations inherent in its nonrandomized, retrospective study design. Lack of control group limits objective comparison of mini-monovision method to standard bilateral implantation of EDOF targeting emmetropia. Furthermore, the absence of defocus curve testing after surgery limits the analysis of continuous visual function following mini-monovision approaches with intended residual myopia in both eyes. Previous study on ZXR00 mini-monovision with dominant eye targeting emmetropia and nondominant eye targeting residual myopia have shown considerable shifts in binocular defocus curve compared to those of dominant and nondominant eye after surgery [20,33]. It has shown that defocus curve of the nondominant eye had unimodal shape similar to that of the dominant eye, but with a rightward shift of roughly −0.5 to −0.75 D reflecting the intended myopic target [20]. The binocular defocus curve has demonstrated a larger landing zone that encompasses both dominant and nondominant defocus curves [20]. A recent study [33] comparing the ZXR00 mini-monovision method to the standard non-mini-monovision method also showed a similar pattern. The mini-monovision group’s binocular defocus curve had a less steep decline and better VA at all defocus levels than both dominant and nondominant monocular defocus curves. It also shows superior VA in the −1.5 to −3.5 D defocus range compared to the binocular defocus curve of the non-mini-monovision group. Future research will require defocus curve tests using ZXR00 mini-monovision method that target the dominant eye with slightly myopic refraction to evaluate the visual performance of different mini-monovision methods. Another weakness of the paper is that there was no investigation of patients’ satisfaction scores. Lastly, the study only looked at outcomes at 3 months and 2 years postoperatively. Further studies with regular 3-month examinations would be able to provide a more specific picture of VA trends following mini-monovision method.
In summary, the bilateral implantation of ZXR00s with mini-monovision leads to an outstanding range of VA from far to near, allowing high spectacle independence. These results have been successfully maintained for 2 years.
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